By Clare Murphy
BBC News health reporter
The Department of Health recommends exclusive breastfeeding for six months
Doctors are launching the first study to establish how many breastfed babies fall dangerously ill after failing to take in enough milk.
Information about the number of seriously dehydrated newborns readmitted to hospital will be gathered across the UK and Irish Republic.
Severe hypernatraemic dehydration is a rare but potentially fatal condition.
It has been suggested that the number of cases may be rising as more women heed the "breast is best" message.
Localised studies suggest some hospitals treat a baby a week for anything from mild to severe dehydration, but there is a lack of comprehensive data for the medical community to work from - and act upon.
"People are very cagey about saying anything that might give breastfeeding a bad name," says Dr Sam Richmond, a consultant neonatologist at Sunderland Royal Hospital.
"There has become something of a religious affiliation to breastfeeding," he added, "and perhaps a desire not to rock the boat for something which is rare.
"But it does need to be addressed - and properly studied - because the consequences can be so severe."
Hypernatraemic dehydration occurs when babies fail to take in sufficient quantities of milk in the early days of life.
The levels of sodium in their blood rise dramatically, and if untreated, this can lead to seizures, gangrene, brain damage - and in the worst cases, death.
If picked up soon enough, the effects are easy to reverse with a steady process of rehydration, but it is not always easy to spot as babies can look pink and alert while being on the verge of becoming critically ill.
The serious cases recorded in the UK tend to involve first-time mothers who are highly motivated to breastfeed.
Current Department of Health advice urges women to nurse their infant exclusively for the first six months. It notes the benefits of breastfeeding include protection for the baby from certain infections, and for the mother from some diseases in later life.
Less than 1% of women actually breastfeed their baby exclusively for this long, and NHS research suggests a significant number experience problems in the first few weeks - with insufficient milk supply and baby's failure to suckle properly cited as the main problems.
There have also been moves to discourage formula feeding: advertising is not allowed and some hospitals restrict formula milk on the ward.
Over the course of 13 months, doctors across the UK and Ireland will be asked by the British Paediatric Surveillance Unit every four weeks to report the number of babies they have seen with severe hypernatraemic dehydration.
Dr Sam Oddie, a consultant in the neonatal unit at Bradford Royal Infirmary, is leading the study.
"Once we understand the scale of the problem we can work out what to do about it - how to spot it, and how to act on it," he said.
"But as far as I'm concerned the answer isn't more formula feeding, but increased support for breastfeeding from the outset in the form of counsellors.
"Women who are having difficulties should be monitored and helped - this is something society really needs to invest in."
Tipping the scales
Unicef's UK Baby Friendly Initiative also called for women to be given more assistance in establishing successful breastfeeding.
"Unfortunately many health workers are unable to give this support, or notice when things are going wrong, as they have not had adequate training and appropriate practices and policies are not in place," says director Sue Ashmore.
Doctors also urge that a consistent early weighing programme be introduced to pick up cases of dehydration.
Research suggests babies who lose more than 10% of their birth weight should be routinely referred, as this is a marker that something may be wrong.
There has never been a uniform newborn weighing policy in the UK - and more frequent measurements may increase the burden on already overstretched community midwives.
There are also concerns that regular weighing in the early days of life may put mothers off breastfeeding as such infants tend to lose significantly more weight - and gain it more slowly - than their bottle-fed contemporaries.
But it would be a failure of care, according to at least one paediatrician, to let fears that mothers may abandon breastfeeding get in the way of a programme which could save lives.